Conventionally, centrifugal fans provided in air conditioners and the like have been designed to promote cooling of fan motors in order to prevent overheating of fan motors during operation.
The following explains a conventional ceiling-embedded air conditioner provided with a conventional centrifugal fan that has a fan motor cooling mechanism to promote cooling of the fan motor of the centrifugal fan.
The air conditioner includes a casing that houses various constituent equipment, and a decoration panel arranged on the lower side of the casing. An air inlet is provided at the approximate center of the decoration panel. The casing is provided therein with a centrifugal fan that sucks in air from the air inlet and blows it out in the outer peripheral direction, and a heat exchanger arranged so that it surrounds the outer periphery of the centrifugal fan.
The centrifugal fan has a fan motor that is fixed at the approximate center of the top plate of the casing, and an impeller that is rotationally driven by the fan motor. The impeller principally includes a hub that is coupled to the shaft of the fan motor, a shroud that is arranged spaced apart by a prescribed spacing on the side opposite the fan motor of the hub (namely, the air inlet side), and a plurality of blades arranged between the hub and the shroud and arrayed in the circumferential direction. An opening is provided at the approximate center of the shroud so that it opposes the air inlet. In addition, the hub has a plurality of cooling air holes positioned on the outer peripheral side of the shaft and the inner peripheral side of the plurality of blades. In addition, the inner peripheral part of the hub bulges towards the side opposite the fan motor, and the fan motor is arranged so that it opposes that bulged portion. Furthermore, a hub cover is provided on the surface of the hub on the side opposite the fan motor that covers the cooling air holes in a state spaced apart by a prescribed spacing from the hub. The surface of the hub cover on the hub side has a plurality of guide blades provided so that they protrude radially.
At the centrifugal fan, air is sucked from the rotary shaft direction into the interior of the impeller via openings in the air inlet and the shroud. Further, the orientation of the flow of that sucked in air changes to a direction that intersects the rotary shaft, and that air is blown out toward the outer peripheral side of the impeller by the plurality of blades. A portion of the air blown out toward the outer peripheral side of the impeller passes through the vicinity of the fan motor and cools the fan motor due to the difference in the static pressure of the space on the fan motor side of the hub and the static pressure of the space on the side of the hub opposite the fan motor (space inside the impeller), and is subsequently blown once again into the space inside the impeller via the cooling air holes of the hub. At this time, the air being blown out from the cooling air holes is easily guided to the space inside the impeller by the ventilation action of the guide blades of the hub cover. Consequently, the quantity of air blown out from the cooling air holes increases, making it possible to increase the cooling effect of the motor (e.g., refer to Japanese Patent Application Kokai No. HEI 11-101194).
The abovementioned conventional centrifugal fan can increase the quantity of air blown out from the cooling air holes by radial guide blades provided in the hub cover, but there is a tendency for the noise level to increase.